Catalytic processes for the conversion of hydrocarbons are well known and extensively used. Invariably the catalyst used in these processes become deactivated for one of more reasons. Where the accumulation of coke deposits causes the deactivation, reconditioning of the catalyst to remove coke deposits restores the activity of the catalyst. Coke is normally removed from catalyst by a regeneration operation that contacts the coke containing catalyst at high temperature with an oxygen-containing gas to combustively remove the coke. Regeneration may be carried out in-situ or the catalyst may be removed from a vessel in which the hydrocarbon conversion takes place and transported to a separate regeneration zone for coke removal. Arrangements for continuously or semi-continuously removing catalyst particles from a reaction zone for coke removal in a regeneration zone are well known.
In order to combust coke in a typical regeneration zone, a recycle gas is continuously circulated to the combustion section and a flue gas containing by-products of a coke combustion, oxygen, and water is continually withdrawn. Coke combustion is controlled by recycling a low oxygen concentration gas into contact with the coke-containing catalyst particles. The flue gas/recycle gas is continuously circulated through the catalyst particles. A small stream of makeup gas is added to the recycle gas to replace oxygen consumed in the combustion of coke and a small amount of flue gas is vented off to allow for the addition of the makeup gas. The steady addition of makeup gas and the venting of the flue gas establishes a steady state condition that produces a nearly constant concentration of water and oxygen as well as the combustion products in the recycle gas.
In continuous or semi-continuous regeneration processes, coke laden particles are at least periodically added and withdrawn from a bed of catalyst in which the coke is combusted. Regions of intense burning that extend through portions of the catalyst bed develop as the coke is combusted. After this intense burning, certain catalysts require reconditioning to restore its effectiveness. For example reforming catalysts typically contain chloride compounds and noble metals, usually platinum. These catalysts require reconditioning to restore the activity of the noble metal to its most highly catalytic state and to replace chloride on the catalyst that may be lost in the reaction zone or through the combustion of coke. Reconditioning for a reforming catalyst will include contact with a chloride containing compound, to redistribute the platinum metal and replace the chloride that may be lost from the catalyst, followed by a drying step to reduce the moisture content of the catalyst and finally a reducing step to change the platinum metal from various oxidized states to a reduced metallic condition.
A number of environmental and operational problems have been associated with these catalyst reconditioning steps. Replacing chloride on the catalyst and re-dispersing platinum over the surface of the catalyst are both done in the presence of a chloride compound. The catalyst platinum redispersion benefits from a high chlorine environment. The chlorine and hydrogen chloride in the chloride contact zone are in equilibrium with the water and oxygen present herein. This equilibrium is skewed towards higher concentrations of hydrogen chloride. In order to provide adequate chlorine for redispersion of the platinum metal, the total concentration of hydrogen chloride must be relatively high. Maintaining the high hydrogen chloride environment adds to the expense of designing the regeneration zone by requiring the recycle of hydrogen chloride-containing gas. In most cases, this recycle of the gas is done by a closed loop system, a heater, a blower and associated piping. The expense of this equipment is compounded by the fact that exotic materials are needed to withstand a hydrogen chloride environment. Moreover, gas must be vented from the halogenation loop that circulates the hydrogen chloride containing gas. This vented gas has a high concentration of hydrogen chloride and must, therefore, be vented or treated in a way that avoids damage to equipment or the environment. Another drawback associated with the high hydrogen chloride environment is that there is often more hydrogen chloride uptake on the catalyst than is necessary or desired.
This invention provides a method of reactivating a noble catalyst that has been deactivated by the accumulation of coke on its surface and requires regeneration to remove coke and contact with a chlorine containing compound to restore adequate catalytic activity. This invention is particularly suited for catalysts that use platinum metals and maintain a chloride concentration on the catalyst particles. In such cases, the arrangement and operation of this method and apparatus will improve the redispersion of platinum on the catalyst particles and allow a better control of the chloride content on the reconditioned particles. This invention can also reduce emissions and handling problems associated with hydrogen chloride containing gases and can reduce the overall expense of operating a regeneration zone for the reconditioning of such catalyst particles.